I think it would be nice if we pulled all of these AST classes that we reference into a data structure at the top of the file? Something like...

```ruby
AST_CLASSES = if ENV['USE_LEGACY] 
  {
    :scenario => Ast::Scenario,
    :scenario_outline => Ast::ScenarioOutine,
    :table => Ast:Table
  }
else
  # ...
end
```

We can then use that to select the correct class as needed in the code? WDYT?